Antenna



y 1', 1941- H. H. BEVERAGE 2,2 4

ANTENNA Filed Dec. 10.1.938

ATTORNEY.

I I NV EN TOR. M210 H. BEVERAGE.

Patented July 1,1941

ANTENNA Harold Hi Beverage, Riverhead', Y.,I assignorto RadioCorporation of America, a corporation of I Delaware Application December10, 1938, Serial INo; 244,897

scam.

. The present invention relates toshort wave antennas and, moreparticularly, to antennas for receiving horizontally polarized wavesover awide band of frequencies.

Anobject of the present invention is to enable the reception ofhorizontally polarized signals over a wide band of frequencies such-asis at present used in television,

.Another object of the invention is to provide a wide band receivingantenna for horizontally polarized signals. 7

Still another objectof my invention isto provide an antenna having ahorizontal directivi-tydiagram which is uni-directional.

The foregoing objects and others. which may appear from the followingdescription: are ac-.

complished by providing a circular or rectangular single turn loopantenna with a damping; re-

sistance at its center equal to the-surge impedance of the loop in orderto make it aperiodic. The loop antenna is arranged in; a horizontalplane. If the diameter of the loop is' substantially less than half thelength of the operating wave the directive pattern is substantiallyuni-directional. having somewhat the shape of a cardioid.

A more complete understanding of the invention will be had by referenceto to the following detailed description which is accompanied by' adrawing in which Figure 1 illustrates a preferred form of my antenna;Figure 2 illustrates a; modia further modification of my invention andFigure 4 illustrates the directive diagram of the antennas showninFigures 1 to 3. 1 a

Figure 1 shows a receiver l-connected'by means of transmission line TLtomy loop antenna, the antenna being denoted by the reference numeral 3.The diameter of the antenna is preferably made somewhat less than a halfthe length of the operating wave. The loop may be constructed of coppertubing and arranged to be practically self-supporting. As an example,one-half inch tubing may be used, formed into a circle having a diameterof .966 meter. At the side of the loop opposite the transmission line isconnected a damping resistor 2' as shown in the figure and which, in theexample given, may have a value of 700 ohms. Assuming that the antenna 3is arranged in a horizontal plane and that a horizontally polarized waveis arriving at the antenna in the direction indicated by arrow B, avoltage is induced in branches nhf and mac in the same direction asindicated by the arrows I. The voltage induced in any elemental portionof the antenna such as g or h, for example, causes 3U fication thereof,while Figure 3 illustrates, still.

a:currentto-startflowing in both directions. Due

to: the damping resistance 2 the currents flowing toward m andn are notreflected and never reach the transmission line TL at ab. The onlyenergy that" reaches the transmission line is that traveling towarde andAs soon as the wave in space Y has progressed beyond points e and f onthe antenna, the direction of the induced voltage is reversed sinceconductors ac and bf are sloped in a direction opposite to conductors emand in with respect-to a wave traveling in the direction BLConsequently, the voltage induced in conductors ac and bf is equal toand is degrees out'of phasewith the component of the voltageinduced inconductors em and In and which is traveling" towards the-transmissionline TL at ab". Hence, no voltage from the direction B reaches thereceiver lfor any frequency lower than the frequency for which thedistance ma is less than half the wave length. I

Now, consider a wave arriving at the antenna and traveling in'thedirection indicated by the arrow: A. The elemental voltages induced inconductors em and in. now have to travel back through the conductortowardsthe transmission line in the direction opposite to the directionof travel of the oncoming wave. 'Ihisintroduc'es a time delay whichshifts the phase ofthe energy from conductors em and In. so that by thetime itreaches the transmission line ab it is no longer cancelled by theenergy induced in conductors aeand bf. In fact, whenthe length of theconductors fromg to c approach a length of onetraveling (in thedirection A.

Figure 2 illustrates a modification of my invention shown in Figure 1wherein instead of my loop being circular in form it is approximatelyrectangular. The distance across the corners of a rectangle is still tobe considered as somewhat less than a half the length of the operatingwave. In such case, the modification shown in Figure 2 operatessubstantially as described for the embodiment shown in Figure 1.

The further modification of my invention shown in Figure 3 embodies arectangular antenna with the sides respectively at right angles andparallel to the direction of travel of waves arriving from A and B. Thedistance between conductors ca, bd and gm, nh is preferably a quarter ofthe length of the operating wave. Thus, for a wave traveling in thedirection indicated by arrow B the voltage induced in ca and bd is equalto and opposite in phase to the voltage induced in gm and nh. On theother hand, for a wave traveling in the direction indicated by arrow A,a phase difierence exists because of the time it takes for the wave toreach conductors gm and nh and the time it takes for the induced voltageto flow back to the transmission line through conductors cg and dh.Since the length of these conductors is a quarter of alength of theoperating wave, a wave traveling in the direction indicated by the arrowA will reach conductors gm and nh a quarter wave, or 90 degrees inphase, later than it reaches conductors ca and bd. The voltage inducedin conductors gm and nh is delayed another quarter wave, or 90 degrees,in traveling back through the conductors cg and hd. Consequently, thetotal phase shift is 180 degrees which brings the energy from gm and uh.into phase with the energy from ca and bd at the receiver I.

From the foregoing description it will be seen that this antennaoperates as a uni-directional antenna for any frequency higher than thatfrequency for which the dimension of the antenna in the direction ofwave travel is substantially less than a half wave length giving adirectional diagram as shown in Figure 4, wherein the direction ofmaximum sensitivity of the antenna is from the side to which thetransmission line is connected. In an antenna constructed according tothe example given above this directional diagram was practicallyconstant over a frequency range from 45 megacycles to 100 megacycles.

While I have particularly shown and described several modifications ofmy invention, it is to be particularly understood that my invention isnot limited thereto but that modifications may be made within the scopeof the invention.

I claim:

1. A broad band short wave antenna comprising a single turn horizontalloop, a transmission line connected to one side of said loop, aresistance serially connected in said loop opposite said transmissionline, the dimension of said loop between points on said loop midwaybetween said resistance and said transmission line being less than ahalf length of the operating wave such that said loop has a maximumresponse in the direction of said transmission line and a lesserresponse in every other direction.

2. A broad band short wave antenna comprising a single turn horizontalloop, a transmission line connected to one side of said loop and adamping resistance serially connected in said loop opposite saidtransmission line, the

dimension of said loop between points on said loop midway between saidresistance and said transmission line being between the limits ofone-third and one-seventh of the length of the operating wave such thatsaid loop has a substantially uniform response in one direction for awide band of frequencies and a smaller response over said wide band inevery other direction.

3. A broad band short wave antenna comprising a single turn horizontalloop, a transmission line connected to one side of said loop and adamping resistance serially connected in said loop opposite saidtransmission line, the transverse dimension of said loop being on theorder of one meter whereby substantially uniform response in onedirection is obtained for frequencies between the limits of 45 andmegacycles and a smaller response over said band in every otherdirection.

4. A broad band antenna comprising a pair of substantially semi-circularconductors arranged about a common center in a horizontal plane, theradius of curvature of each of said conductors being less thanone-quarter the length of the operating wave, a transmission lineconnected to one pair of adjacent ends of said conductors and a dampingresistance connected across the other pair of adjacent ends.

5. A broad band antenna comprising a pair of substantially semi-circularconductors arranged about a common center in a horizontal plane, theradius of curvature of each of said conductors being less thanone-quarter the length of the operating wave, a transmission lineconnected to one pair of adjacent ends of said conductors and a dampingresistance connected across the other pair of adjacent ends, saiddamping resistance having a value equal to the surge impedance of theloop.

6. A broad band antenna comprising a pair of linear conductors eachhaving a length less than half the length of the operating wave, saidconductors lying in a common horizontal plane and spaced apart adistance equal to a quarter of the length of the operating wave,connections between the ends of said conductors, a transmission lineconnected to the center of one of said conductors and a dampingresistance serially connected in the center of the other of saidconductors the length of said conductors and the spacing therebetweenbeing such that said antenna has a maximum response in the direction ofsaid transmission line in the plane of said antenna and a lesserresponse in every other direction in said plane.

HAROLD H. BEVERAGE.

